The sustained antiviral response of chronic HCV infection has been improved recently by the use of the protease inhibitor (telaprevir or boceprevir) along with interferon alpha (IFN-) and ribavirin. However, results of recent clinical trials indicate that the final outcome of triple combination therapy is strongly dependent on the patient's initial response to IFN- plus ribavirin and the host genetic variation of IL-28 gene polymorphism. The biological mechanisms underpinning this association remain unknown. The current application explores mechanisms for how the IFN-? axis is linked to the success of IFN-/ribavirin treatment using a stable and persistently infected HCV cell culture system. The proposal is based on several exciting and encouraging preliminary studies. We have developed a persistently HCV infected cell culture system that supports high- level viral replication to address the antiviral mechanisms of IFN- and ribavirin combination treatment. We reported that HCV infection itself induces ER-stress and autophagy response that selectively down regulates the type-I IFN receptor but not the type-II or type-III IFN receptor, impaired Stat1/Stat phopshorylation, nuclear translocation, defective Jak-Stat signaling and impaired antiviral response. We have reported that ribavirin and IFN each inhibit HCV IRES translation and synergistically inhibit HCV replication. The ribavirin resistance mechanism relates to the impaired ribavirin uptake due to the down-regulated expression nucleoside transporters in HCV cell culture. Our results indicate that IFN-? has a strong antiviral action against HCV and it clears HCV replication to a completion in Jak-Stat defective and persistently infected HCV cell culture system through activation of Stat3, AKT and MAPK pathways suggesting that the type III IFN system plays a very important role in the clearance of HCV infection. In this R01 application, we will focus on understanding the mechanism underlying the association between IL28B polymorphisms and IFN-/ribavirin antiviral mechanisms of HCV infection in a persistent infectious cell culture system in hepatocyte cell lines with a different genetic background of IL-28B gene. Our hypothesis is that hepatitis C virus infection itself creates defective Jak-Stat signaling by down regulating the expression of IFNAR1 that leads to impaired response to pegylated IFN- and ribavirin. To test this hypothesis we propose the following three Specific Aims. Aim 1: To test hypothesis that the IFN-? axis is important for HCV clearance and treatment using a persistently infected HCV cell culture. Aim 2: Study the mechanisms by which IFN-? overcome IFN- resistance of persistent HCV infection. Aim 3: To investigate the synergy and resistance mechanism of ribavirin in HCV infection. Since IFN-? clears HCV replication in Jak-Stat defective IFN- resistant cells, understanding the signal transduction and anti-viral mechanism of IFN-? proposed in this grant application should open novel strategies for the treatment of chronic HCV infection.